This invention generally relates to the field of semiconductor device manufacturing, and more particularly, to reflow furnaces and the processing of semiconductor devices in reflow furnaces.
In the manufacture of semiconductor devices, components are conventionally joined together by soldering. In order to efficiently solder in a production environment, solder reflow furnaces are used. In a solder reflow furnace, semiconductor components are placed on a conveyer belt and conveyed through a tunnel-type furnace. The semiconductor components are heated to above the melting point of the solder while in the furnace, permitting the solder to flow and to bond the parts. To provide a good solder joint the solder is typically heated to about 50xc2x0 C. above its melting point. Solder reflow furnaces are usually operated at temperatures from about 200xc2x0 C. to about 400xc2x0 C.
Typically, reflow furnaces are heated by either a hot gas or infrared radiation. In general, then, solder reflow furnaces can be classified as radiation-types or hot gas-types. The radiation-type reflow furnace is one in which a number of paneled heaters are disposed in the upper and lower portions of a tunnel and semiconductor devices are heated by the heat radiated from the panel heaters. The inside of the furnace is heated to a suitable temperature for soldering by controlling the current supplied to the panel heaters. The radiation emitted from the panel heaters can either be near or far infrared radiation.
A solder reflow furnace of the hot gas-type is one in which hot gas is circulated past a heater providing a constant heating temperature. Typically, nitrogen is the gas of choice in a reflow furnace. However, other inert gases can also be used, as well as hydrogen. Although nitrogen is not a class VIIIA element, as used herein nitrogen will be considered an inert gas. Inert gases and hydrogen are used in both hot gas-type and radiation-type reflow furnaces to limit the amount of oxygen present in the furnace. Low oxygen levels are desirable to prevent oxidation of the components being soldered.
Fluxes are used with solder to promote soldering. When the solder is heated, the flux is evaporated and the solder fumes are carried by the gas circulating in the furnace. The evaporated flux is carried out through the furnace exhaust pipe. In a high volume production environment, flux effluent condenses on the inside wall of the furnace exhaust pipe. As the build-up of the flux effluent condensation increases, it starts to drip back into the furnace onto the production parts. The flux will contaminate production parts and cause rejection of the parts. Not only will the semiconductor device become dirty, but the flux causes a decrease in electrical resistance, corrosion, and other problems which adversely affects the electrical components of the semiconductor device.
There exists a need in the solder reflow art to control and/or eliminate the problem of flux dripping back into the solder reflow furnace and contaminating semiconductor devices.
This and other needs are met by embodiments of the present invention which provide a solder reflow furnace comprising: a heater that heats the solder reflow furnace to an operating temperature, a conveyor that conveys semiconductor devices through the solder reflow furnace, an exhaust opening for venting gases from the solder reflow furnace and a flux effluent collector connected to the exhaust opening.
The earlier stated needs are also met by another embodiment of the present invention which provides a device for preventing flux drip-back into solder reflow furnaces comprising: a solder reflow furnace exhaust pipe and an exhaust gas heater and flux cooler both positioned on the exhaust pipe. A flux condensation region of the exhaust pipe is located adjacent to the flux cooler. A flux drain conduit connects the flux condensation region to a flux collection container.
The present invention also provides a method for preventing flux contamination of semiconductor devices. Semiconductor devices are conveyed through a solder reflow furnace having an exhaust opening and a flux effluent collector. Gas flows through the solder reflow furnace, wherein at least some of the gas exits the furnace through the exhaust opening and flux effluent collector. The gas which passes through the flux effluent collector is heated to maintain flux effluent carried in the exhaust in a gaseous state. Subsequently, the exhaust gas is cooled in a flux condensation region to condense the flux effluent. Then, the condensed flux is collected in a manner such that the condensed flux does not re-enter the reflow furnace.
The solder reflow furnace of the present invention provides cleaner semiconductor devices with higher yield. The solder reflow furnace arrangement prevents flux drip-back into solder reflow furnaces. In addition to a higher yield of cleaner parts, the present invention also provides for disposing of flux effluent in an ecologically sound manner.
The foregoing and other features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.